Auxiliary reamplification radio circuits



I7, 1936. -R 2,934,548 AUXILIARY REAMPIJIFICATION RADIO CIRCUITS Filed Oct. 2, 1930 4 Sheets-Sheet l o J 19 I I whf 1 Q. ATTORNEY;

F. ZlDAR AUXILIARY REAMPLIFICATION RADIO CIRCUITS l rch 17, 1936.

Filed Oct} 2, 1930 4 Sheets-Sheet 2 SQQ NQ xg INVENTOR ATTO RNEYS 17, 1935. Z|DAR AUXILIARY REAMPLIFIGATION RADIO CIRCUITS Filed Oct. 2, 1930 4' Sheets-Sheet 3' ATTO RNEYS AUXILIARY REAMPLIFICATION RADIO CIRCUITS R A m 2 F.

' 4Sheets-Sheet 4 Filed Oct. 2, 1930 ATTORNEYS Patented Mar. 17, 1936 UNITED STATES PATENT OFFICE AUXILIARY REAMPLIFICATION RADIO CIRCUITS 6 Claims.

The present invention relates to a new and improved radio circuit receiving signal energy from a dual antenna system having horizontally disposed aerials preferably located at right angles to each other. The invention also relates to means for producing super amplification of the energy utilized in the transmitting apparatus used by radio and television broadcasting systems.

My object in developing this circuit, which embodies what might be called a straight line or direct system of energy amplification combined with an indirect or auxiliary system involving one or more stages of energy reamplification was to secure a more effective utilization of radio energy.

With circuits embodying my invention there is a very considerable increase of signal energy amplification above that which is characteristic of other circuits, greater amplification being brought about by use of my indirect or auxiliary reamplification system, wherein inductively-generated energy may be said to be independently amplified and then returned to the direct or straight line system at the radio-frequency end of the circuit.

Of the accompanying drawings, similar parts are identified by the same references,

Figure 1 is a circuit diagram of the present system;

Fig. 2 is a circuit diagram exactly like Figure 1 except that capacity tuning by means of variable condensers is employed;

Fig. 3 is a circuit diagram showing a reamplification line inductively coupled to the main-line system beyond, or following the point of detection;

Fig. 4 is a circuit diagram exactly like Figure 3 except that variable condensers are used for tuning and balancing;

Fig. 5 is a circuit diagram similar to Figure 1 but differing therefrom in that it embraces three stages of radio frequency amplification instead of two;

Fig. 6 is a circuit diagram like that of Figure 5 but showing the application of variable condensers instead of variable inductance units for tunmg;

Figs. '7, 8, and 9 are schematic diagrams rough- 1y indicating the up-building and transfer of energy in circuits represented by Figs. 5, 3, and 1 respectively.

Figure 1 shows a circuit embodying one of numerous possible applications of my invention, the

. direct or straight line energy-amplifying elements of the circuit being represented by the first tuning-unit transformer (comprising inductances 4, 5, 6, and 1), first radio-frequency tube IRF, primary winding of first reamplifying transformer lReT, second tuning unit transformer (comprising inductances 8, 9, l0, and II) second radiofrequency tube 2RF, primary of second reamplifying transformer ZReT, air-core transformer (comprising primary and secondary inductances I2 and I3) detector tube DET, audio transformer AT and audio amplifying tube and thence to recording device.

The indirect, subsidiary, or auxiliary, energyreamplifying system comprises two transformers inductively and conductively related to the direct or straight-line amplifying system, two reamplifying tubes having grids connected to the secondary winding of the transformers and plates connected to reamplifying inductances forming part of two tuning-unit transformers having twopart secondaries of which one part (outer) is axially shiftable for tuning, variable resistances being connected across the ends of the reamplifying inductances, as indicated.

Insertable after any stage of amplification both prior to and following detection in the direct straight-line system, wherein the signal energy is amplified progressively in the usual manner, each reamplifying tube and transformer to which it is connected form part of a reamplification system but slightly dependent for energization on the direct or straight line system to which the auxiliary reamplifying system is both conductive- 1y and inductively connected, amplified signal en-- ergy picked up by the fixedly positioned tapped secondary ll! of the right-hand or second tuningunit transformer being fed back through the secondary winding of the first reamplifying transformer lReT to the grid of the first reamplifying tube IReA, from the plate of which the reamplified energy passes to the reamplifying inductance 5 of the first tuning unit transformer through the variable resistance shunted across its ends, the reamplifying inductance lying alongside of and below the first tuning unit transformer primary inductance, to which one of two antennas is connected, as indicated by Figs. 1, 3 and 5.

Fig. 2 shows the application of my invention to a capacity-tuned circuit exactly like that shown in Fig. 1 except for the method of tuning which is by means of variable condensers instead of byvarying inductive relationships.

It will be noted that with this circuit, as with that illustrated by Fig. 1, No. l antenna supplies signal energy to the upper primary inductance 4 of the first tuning unit transformer, the stationary secondary winding 6 of which is connected to the grid of the first radio-frequency tube, IRF, the output of which passes through the primary winding of the first reamplifying transformer lReT and thence through upper primary inductance 8 of the second tuning unit transformer, the stationary part 10 of the secondary inductance of which is tapped and connected'to the secondary winding of the first reamplifying transformer IReT, which in turn is connected to the grid of the first reamplifying tube, the output of which is returned to the lower reamplifying inductance through a variable resistance shunted across its ends, exactly as in Fig. 1, the reamplifying inductance lying alongside of the upper primary inductance 4 forming part of the tuning unit transformer, to the movable secondary inductance 1 of which antenna No. 2, preferably at right angles to No. I antenna, is connected.

Figs. 1 and 2 show two stages of straight-line or direct radio-frequency amplification and two auxiliary stages of indirect re-amplification before detection, while Figs. 3 and 4 show two stages of straight-line or direct radio-frequency amplification combined with one stage of indirect reamplification before and one after detection, the means and method of securing re -amplification constituting the so-called auxiliary or indirect system that characterizes my invention, which resides in the combination of said means and method of developing and applying inductivelyproduced re-amplifying energy with commonly used means and methods for amplifying the signal energy picked up by the antenna.

Fig. 5 represents a hook up embracing a dual unit single-control vario-selector tuning device of inductive type, as illustrated and described in my copending application Serial Number 475,862, issued March 6, 1934, Patent No. 1,949,733, the circuit having three stages of direct or straightline radio-frequency amplification instead of two, as in Figs. 1 and 2, and two stages of inductivelyproduced re-amplification prior to detection, the output of the second radio-frequency tube 2RF passing through the primary winding of the first reamplifying transformer lReT to the primary inductance I2 of the radio-frequency air core transformer, from whose tapped secondary, or grid coil 13, energy is returned to the secondary winding of the first reamplifying transformer IReT, there uniting with the energy inductively produced therein, thence passing to the grid of the first reamplifying tube lReA, whose output is returned to the reamplifying inductance 5 forming part of the: first or left-hand tuning-unit transformer, the similarly-developed output of the second reamplifying tube ZReA being returned to the reactivating inductance 9 forming part of the second or right tuning-unit transformer.

In all hookups represented by Figs. 1 to 6 inclusive, it will be noted that antenna No. I, is connected to the upper end of the primary inductance 4 of the first or left-hand radio-frequency tuning unit transformer, the lower end of the primary being independently and externally grounded, while antenna No. 2, preferably at right angles to No. l is connected to the movable secondary inductance I of the same transformer,

The radio-frequency tuning-unit transformer primaries 4 are stationary and in close co-axial relationship to surrounding stationary secondaries or grid coils 6, only the outer concentrically disposed part I of the secondary coils being reciprocally movable for tuning. The grid coils of circuits initially tuned by my vario-selector unit are tapped, as indicated by Figs. 1 and 3, to provide an optical antenna connection. The lower ends of grid coils of all the circuits illustrated are grounded within set to A negative, as are also the movable parts 1 of tuning-unit secondaries held in close vario-inductive relationship to stationary parts 6 of secondaries, as is indicated by Figs. 1, 3, and 5, fixed condensers being shunted across the ends of the movable and stationary secondary inductances, as indicated.

In capacity-tuned circuits embodying my invention the lower ends of the tapped secondaries or grid coils 6, I0, and I3 are grounded within set to A negative, variable condensers for tuning and for balancing being shunted across the upper and lower ends of the coils, as indicated by Figs. 2, 4, and 6.

With the circuits illustrated by Figs. 1 and 2 inductive development of reamplifying energy begins immediately upon passages of output energy of first radio-frequencyw tube IRF of straight-line or direct amplification system through the primary winding of the first reamplifying transformer IReT which is part of the auxiliary or indirect amplification system and is interposed between the first radio-frequency tube plate and the primary inductance of the second tuning-unit transformer 2ReT. This energy, together with that supplied from the tapped secondary of the second tuning-unit transformer ZReT, is returned to the grid of the first reamplifying tube I ReA of the auxiliary or indirect amplification system, passing therefrom to the reamplifying inductance 5, inductively reenergizing the secondary coil 6 connected to grid of first radio-frequency tube, I RF, the output of which is thereby enhanced, producing a corresponding effect on the primary inductance 8 and inductive response of coil I0 connected to grid of the second radio-frequency tube 2RF of the direct or straight-line amplification system. Grid coil 10 of the second or righthand tuning-unit transformer secondary and secondary winding of reamplifying transformer IReT are direct or mainline sources of inductively developed energy of main-line frequency additively impressed upon the grid of the first reamplifying tube lReA whose output energy acts inductively upon the grid coil 6 of the first or left hand tuning-unit transformer through coil 5, to which the energy is fed back, the regenerative effect of thus feeding back to the first reamplifying tube IRF some of the inductively-produced energy due to flow of plate output thereof being controlled through variation of the resistance connected across the ends of primary inductance 5, a high degree of signal gain thus being obtained without causing the amplifier tube IRF to spill over into self-sustained oscillation.

In precisely the same manner as with the first tube IRF, the output of the second radio-frequency tube 2RF is passed through the primary winding of a second reamplifying transformer 2ReT, the energy inductively developed in the secondary winding thereof being of higher voltage value than that inductively generated in the first reamplifying transformer IReT, the tapped secondary inductance l3 contributing its quota of inductively developed energy to that passing from the reamplifying transformer secondary to the grid of the second reamplifying tube 2ReA of the auxiliary indirect amplification system. The second reamplifying tube output is returned to the reamplifying inductance 9 of the second or right-hand tuning-unit transformer, there acting inductively to reenergize the secondary coil connected to the grid of the second radio-frequency tube ZRF of the direct or straight-line amplification system.

The plate-circuit frequency being the same as the grid-circuit frequency of tubes IRF and ZRF, the efiect of feeding back to the grids of these tubes the energy inductively produced by flow of the plate-circuit output energy thereof is to build up or reinforce the grid-circuit voltages and correspondingly increase the flow of current in the plate circuits, the regenerative effect produced increasing selectivity and sensitivity as a result of enhancing signal strength at the frequency to which the circuit is tuned, frequencies above and below resonant points not being increased in strength.

The object of connecting the fixedly-positioned secondary winding I II of the second or right-hand tuning-unit transformer in series with the secondary winding of the reamplifying transformer IReT is to secure an additive effect in impressing inductively-developed voltages on the grid of reamplifying tube IReA, a similar effect on grid of reamplifying tube 2ReA being obtained by connecting tapped transformer coil I3 in series with secondary winding of reamplifying transformer ZRe'I.

As with coil I0, the tapped secondary winding I3 of Figs. 1 and 3 serves as a main-line source of inductively-developed energy which is returned to the grid of reamplifying tube ZReA.

Varying the position of point of tapping of secondary windings I0 and I3 serves to increase or decrease the excitation voltage applied to grids of reamplifying tubes IReA and ZReA, the voltage increasing as the point of tapping is moved towards grid end of coils and vice versa.

An energy-transfer diagram that indicates approximately what takes place in circuits represented by Figs. 1 and 2 is presented in Fig. 9, which indicates roughly the relationship between the so-called direct and indirect systemsof amplification, the latter supplementing and greatly enhancing the former.

No attempt has been made to show the effect of amplifying signal energy by passage through the radio-frequency detector, and audio frequency tubes, it being considered sufiicient to indicate signal energy by a dotted line passing straight through all the tubes and mingling with that contributed by the indirect system of amplification.

Fig. 9 indicates that amplified signal energy picked up by the first reamplifying tube is reamplified thereby and is then passed through all the tubes of the circuit, at a value conventionally represented by single long dash and short dash lines marked I picking up its own energy as thus indicated, because of its reamplifying relation to the direct amplification system, reamplifying its own picked-up energy which passes through all the tubes at a value conventionally represented by the double dash and dot line marked 2.

The energy reamplified by the first reactivator tube is picked up by the second reamplifying tube, amplified thereby, and then passed through the second radio-frequency, detector, and audio frequency tubes at a value conventionally represented by a three dash and dot line marked 3. As with the first, so also with the second reamplifying tube, its own energy is picked up and reamplified by it because of its reamplifying 5 relation to the direct amplification system, to which its contribution of energy is made just ahead of the second radio-frequency tube, through which and the succeeding detector and audio frequency tubes it passes to the recording instrumentality with a value conventionally indicated by a four dash and dot line numbered 4.

In most respects the circuits presented in Figs. 3 and 4 are similar to those of Figs. 1 and 2, but the former are characterized by location of one of the reamplifying tubes after the detector, the plate of which is connected to one end of the primary winding of the second reamplifying transformer in series with the audio-transformer primary winding, which in turn is connected to a B positive source of energy under suitable tension or voltage.

Inductively amplified energy from tapped secondary inductance I 3 ahead of the detector, added to that developed in the secondary of the second reamplifying transformer after the detector, is fed to the grid of the second reamplifying tube, the output of which is returned to the reamplifying inductance 9 by which the transformer secondary I0 is reenergized. The circuit of Fig. 3 is inductively tuned by my vario-selector tuning unit, while Fig. 4 shows an exactly similar embodiment of my invention in a circuit tuned by capacity, variable condensers being used for that purpose in the same manner as with the circuits of Figs. 2 and 6.

Not only are the circuits presented in Figs. 3 and 4 characterized by location of one reamplifying tube and associated transformer before and one after the detector, but the transfer of energy from the indirect to the direct amplification system is of an intervolved intermingling, or interlocking character, a feature not present in hookups such as are shown in Figs. 1 and 2, wherein each reamplifying tube and associated transformer may be said to function independently or separately, making a contribution of different value to the flow of energy through the so-called direct or straight-line amplification system.

With the circuits of Figs. 3 and 4 however, there is a transfer of energy corresponding roughly to that indicated schematically by Fig. 8 which shows how the signal energy amplified by the first and second radio-frequency tubes is picked up by the first reamplifying tube, reamplified thereby, and passed through all the tubes of the direct or straight-line amplification system with a value conventionally indicated by a single dash and dot line numbered I, although the so-called value thereof because of greater amplification by reason of passage through the second radiofrequency tube, is somewhat greater than with the similarly numbered energy line of Fig. 9. The first reamplifying tube picks up its own energy, as represented by line No. I, Fig. 8, reamplifies it and returns its reamplified-output to the straight-line amplification system, passing through all of the tubes with a value conventionally indicated by a double dash and lot line numbered 2 but of somewhat higher value than the correspondingly numbered energy transfer line of Fig. 9.

After detection this energy, as well as that represented by line No. I, is picked up by the sec- 75 ond reamplifying tube, reamplified thereby,.and returned to the direct or straight-line amplification system with a value conventionally indicated by the four dash and dot line numbered 4, which passes through the second radio-frequency, detector, and audio frequency tubes to the recording device.

Since all the energy passed through the second radio-frequency tube is picked up by the first reamplifying tube, as indicated by the dotted line bracket that connects energy lines I 2, 3, and 4 at the conventionally represented point of pick up, after the second radio-frequency tube, reamplification thereof and return of the reamplified energy to the direct amplification system with straight-line or No. 5 value through the first radio-frequency and succeeding tubes, provides for the second reamplifying tube another line of energy (5) to be picked up and reamplified thereby to produce an energy value conventionally represented by the double-thick straight line numbered 6 returned to the straightline amplification system through the second radio-frequency tube, passing through detector and audio-frequency tubes to the recording device.

Comparison of the schematic energy-transfer diagrams presented in Figs. 7 and 8 reveals the fact that the principal difference between them involves the relationship of the indirect amplification system to the detector of the direct or straight line amplification system, Fig. 7 representing roughly the energy transfer in a circuit such as that illustrated by Fig. 5 wherein all reamplified contributions of energy to the straightline amplification system are made before detection on anintervolved relationship application of reamplifying tubes and associated transformers similar to that illustrated by Figs. 3 and 4 but with a circuit having three stages of radioirequency amplifications instead of two.

When the direct or straight-line amplification system embraces three radio-frequency stages, as in the circuits represented by Figs. 5 and 6, which are exactly alike except for the means of tuning, which in one case is of inductive type and of capacity type in the other, the intervolved relationship between the direct and indirect amplication systems, as exemplified by conventionally represented energy-transfer diagram of Fig. '7, is especially effective because of superior amplification although but slightly less satisfactory results are obtainable when one of the reamplifying tubes and its associated transformer are inductively energized after detection in the manner illustrated by Figs. 3 and 4, with an energy transfer of the character approximately indicated by Fig. 8 which shows how amplified and reamplified energy modified by detection is returned to the second radio-frequency tube of the direct amplification system wherein reamplifying takes place in passing through succeeding tubes to the recording device.

In explanation of the repeated amplifying activity of the reamplifying tubes that constitute one of the three principal elements of the socalled indirect or out-of-line amplification system, it should be said that these tubesreach their maximum reamplifying capacity only when they pick up and reamplify their own previously picked up energy, the reenergizing effect of which is inductively impressed on the direct or straightline amplification system through the reampliiying inductances 5 and 9 associated with the means employed for tuning the circuit.

With my improved'method of amplification the output of the radio-frequency tubes may be said to undergo a sort of regenerative process where- 'by succeeding tubes are furnished with an abnormally reinforced input a part of the energy produced by inductive response thereto being utilized to reinforce the energy inductively developed in the secondaries of reamplifying transformers, whose output is fed to the grids of the 'reamplifying tubes.

With Fig. 6 only that part of the circuit embracing the variable tuning and balancing condensers is shown, all other features of the circuit being exactly like those to the right of line 6-6 of Fig. 5, the energy-transfer diagram, Fig. 7, applying to both inductively-tuned and capacitytuned circuits.

Of the accompanying drawings, Figs. 1 to 6 inclusive indicate that the plates of the reamplifying tubes are connected to tuning-unit reamplifying inductances through potentiometers conventionally represented as variable resistances shunted across their ends, the inductances being connected, as indicated, to a common source of plate potential of suitable value, which may be different from that on the plates of the other tubes.

The reamplifying tubes interposed between any two tubes of the straight line amplification system make substantial contributions to the inductively-produced energy carried forward to the recording instrumentality by which the effect of such reinforcements of energy is audibly or visibly expressed.

With my inductively tuned circuit positiona variability of the tuning-unit transformer secondaries obviates the need for balancing means such as characterizes capacity tuned circuits, as in Figs. 2, 4, and '6. There is also a greater range of variability and therefore of tuning capacity with my inductive type of dual-unit tuning device, the axial movement of the tuning-unit secondaries being greater than is the rotary movement of variable condensers, the whole dial range of 360 degrees being available for distribution of the wave lengths to which my circuit is tunable.

Schematicdiagrams 8 and 9 serve roughly to indicate the transference of energy in circuits represented by Figs. 3 and l, the direct amplification system being practically the same in both cases, while the auxiliary reamplification systems are slightly different, the auxiliary reamplification taking place before as well as after etection in Fig. 3 circuit and wholly before detection in Fig. l circuit.

Study of Figs. '7, 8, and 9 brings out the fact that the transfer of energy from the indirect to the direct amplification system may be said to be of a circulatory character in approximately the same sense that water in a boiler or steam in a heating system circulates and recirculates under conditions peculiar to the application and distribution of heat energy.

' With Figs. 7 and 8, which conventionally represent the intervolved energy transfer in circuits wherein the reamplifying tubes and associated transformers are installed before detection, as well as before and after detection, initial circulation of energy takes place through the first and second radio-frequency tubes and first reamplifying tube back to the straight line amplification system from which the circulatory journey began with the picking up of signal energy amplified by passage through radio-frequency tubes. What maybe termed recirculation takes place when the first reamplifying tube picks up and reamplifies its own energy before reaching maximum reamplifying capacity.

The amplified and reamplified energy discharged from the first reamplifying tube is picked up by the second reamplifying tube whether interposed in the circuit ahead of the detector, as in Fig. 1, or after the detector, as in Fig. 3, the character of the energy impressed on the straight-line amplification system in the latter case being modified however by detection, neither input nor output of the second reamplifying tube in the circuits of Figs. 1 and 5 being similarly modified.

With the circuit of Figs. 1 and 2 there is less of a recirculatory transfer of energy, as indicated by a comparison of Fig. 9 with Fig. 7, which indicates roughly the energy transfer in a circuit having three radio-frequency tubes in the straight-line amplification system, or with Fig. 8, which presents a similar idea of what takes place when one of the reamplifying tubes and associated transformer are inserted after the detector of a straight-line amplification system having but two stages of radio-frequency amplification prior to detection.

The energy transfer diagrams herein presented necessarily fail to delineate with absolute accuracy just what happens in each circuit, but they serve a useful purpose in showing how the output of the reactivator tubes of the indirect recirculating and reamplifying system is utilized in reenergizing the straight-line amplification system to effect an augmentation of power as roughly represented at the right-hand or recording ends of the diagrams where energy streams, conventionally indicated by lines numbered from i to 6 come together.

Having described my invention in its relation to a radio receiving circuit with sufficient clarity to enable a person skilled in the art to which it relates to understand and make use of it, and having pointed out its adaptability for use in signal transmission systems and for television purposes, what I claim is:

1. In combination, a main line circuit, a transformer in said main line circuit consisting of first and second primary windings and secondary windings, said first primary winding being connected to a source of radio-signal energy, amplifying means in said main line circuit and connected to said secondary winding, a subsidiary line circuit, amplifying means in said subsidiary line circuit, said amplifying means in said subsidiary line circuit being inductively coupled to the amplifying means in said main line circuit whereby the fiow of amplified signal energy in said main line circuit develops energy in said subsidiary line circuit, and a regeneration-controlling variable resistor receiving the output of the amplifying means in said subsidiary line, said resistor being shunted across said second primary winding whereby the inductively developed energy in said subsidiary line circuit is received in said primary winding and acts inductively on said secondary winding to increase the output thereof.

2. In combination, a main line circuit, transformers connected in cascade arrangement in said main line circuit, each of said transformers consisting of first and second primary windings and secondary windings, said first primary winding being connected to a source of radio-signal energy, a plurality of amplifying means in said main line circuit with each respectively connected to the secondary windings of said transformers, said amplifying means being adapted to receive radio-signal energy from respective transformers to progressively amplify the same, a subsidiary line circuit, amplifying means in said subsidiary line circuit, means inductively connecting said subsidiary line circuit amplifying means with one of said main line circuit amplifying means, means conductively connecting said subsidiary line circuit amplifying means to the other of said main line amplifying means, said inductive and conductive connections being adapted to develop energy in said subsidiary line circuit as a result of amplification of radio-signal energy in said main line circuit, and a regeneration controlling variable resistor receiving the output of the amplifying means in said subsidiary line circuit, said resistor being shunted across the second primary winding of one of said transformers whereby energy developed in said subsidiary line circuit is received in said second primary winding and acts inductively on said secondary winding to increase the output thereof.

3. An amplifying system comprising a main line circuit embodying a plurality of amplifiers, said amplifiers being inductively coupled in said main line in cascade arrangement, a subsidiary line circuit, amplifying means in said subsidiary line circuit, means inductively coupling said subsidiary line amplifying means with one of the amplifiers in said main line circuit, means conductively coupling said subsidiary line amplifying means with another amplifier in said main line circuit, a regeneration controlling variable resistor receiving output of the amplifying means in said subsidiary line, and means coupling said resistor with the first amplifier in said mairi line cascade arrangement.

4. An amplifying system comprising a pair of amplifiers, means inductively coupling said amplifiers in cascade arrangement, one of said amplifiers being inductively coupled to a source of radio-signal energy, a subsidiary amplifier, means inductively and conductively coupling the other of said pair of amplifiers .to the subsidiary amplifier, and a regeneration controlling variable resistor coupled to said subsidiary amplifier and to the first mentioned of said pair of amplifiers.

5. An amplifying system comprising a pair of amplifiers, means inductively coupling said amplifiers in cascade arrangement, one of said amplifiers being inductively coupled to a source of radio signal energy, a subsidiary amplifier, means inductively coupling said subsidiary amplifier to the first of said pair of amplifiers, means conductively coupling said subsidiary amplifier to the other of said pair of amplifiers, and a regenerati'on controlling variable resistor coupled to the output of said subsidiary amplifier and to the first mentioned of said pair of amplifiers.

6. In combination, a main line circuit, amplifying means in said main line circuit, said amplifying means being inductively coupled to a source of radio-signal energy, a subsidiary amplifier, means inductively coupling said subsidiary amplifier to said main line amplifying means, means conductively coupling the input of said subsidiary amplifier to said main line amplifying means, and a regeneration controlling variable resistor coupled to the output of said subsidiary amplifier and inductively to said main line amplifying means.

FRANK ZIDAR. 

